1. Field
The present disclosure relates generally to solar cells and, in particular, to forming solar cells that have multiple junctions. Sill more particularly, the present disclosure relates to a method and apparatus for connecting wafers to each other to form solar cell structures.
2. Background
A solar cell is a device that converts energy in light into electricity using a photovoltaic effect. In manufacturing solar cells, it is desirable to increase the efficiency at which solar cells generate electricity from light. Traditional single junction cells have a maximum theoretical efficiency of about 34 percent.
With multiple junctions, solar cells may have increased efficiency. Multiple junctions may be formed by manufacturing the solar cell with multiple subcells connected by junctions, in which each junction generates electricity from a particular wavelength or range of wavelengths of light passed by a subcell.
A multi-junction solar cell may be manufactured by layering different materials on top of each other. The materials may be selected to pass different wavelengths at the different layers in the solar cell.
Manufacturing multi-junction solar cells may involve manufacturing the different layers onto one or more wafers. These wafers are connected to each other to form the multi-junction solar cell. In particular, the wafers are bonded to each other.
One example of a multi-junction solar cell that may involve bonding wafers together is an inverted metamorphic multi-junction (IMM) solar cell. With this type of cell, dissimilar wafers are bonded to each other. Dissimilar wafers are wafers that have different materials from each other. As a result, the lattices of atoms may pull each other because of these differences.
However, direct bonding of these types of wafers may result in undesired inconsistencies. For example, cracks, delamination, or other undesired themes may occur at these temperatures and pressures in which direct bonding occurs.
Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. For example, it would be desirable to have a method that bonds wafers that are dissimilar to each other in a manner that avoids issues associated with the high temperatures that may lead to cracking, delamination, or other undesired inconsistencies in the wafers.